384 research outputs found
An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896
XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the
2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is
just resolved and has an equivalent width of ~170 eV. The broad-band spectrum
is well modelled by a power law slope of gamma ~ 2.03, together with two
blackbody components to fit the soft X-ray excess. Using a more physical
two-temperature Comptonisation model, a good fit is obtained for an input
photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3
and 200 keV. The soft excess cannot be explained purely through the
reprocessing of a hard X-ray continuum by an ionised disc reflector.Comment: 6 pages, 4 figures, accepted by MNRA
Optical variability of the strong-lined and X-ray bright source 1WGA J0447.9-0322
We present the historic light curve of 1WGA J0447.9-0322, spanning the time
interval from 1962 to 1991, built using the Asiago archive plates. The source
shows small fluctuations of about 0.3 mag around B=16 until 1986 and a fast
dimming of its average level by about 0.5 mag after that date, again with small
short term variations. The variability pattern is within the values shown by
other QSOs with long term monitoring, notwithstanding its high X-ray/optical
ratio. We present also its overall SED using literature data and recent
UV-optical SWIFT observations.Comment: 17 pages, 4 figures, accepted by The Astronomical Journal. Table 2
available upon reques
Interpreting Flux from Broadband Photometry
We discuss the transformation of observed photometry into flux for the
creation of spectral energy distributions and the computation of bolometric
luminosities. We do this in the context of supernova studies, particularly as
observed with the Swift spacecraft, but the concepts and techniques should be
applicable to many other types of sources and wavelength regimes. Traditional
methods of converting observed magnitudes to flux densities are not very
accurate when applied to UV photometry. Common methods for extinction and the
integration of pseudo-bolometric fluxes can also lead to inaccurate results.
The sources of inaccuracy, though, also apply to other wavelengths. Because of
the complicated nature of translating broad-band photometry into monochromatic
flux densities, comparison between observed photometry and a spectroscopic
model is best done by comparing in the natural units of the observations. We
recommend that integrated flux measurements be made using a spectrum or
spectral energy distribution which is consistent with the multi-band photometry
rather than converting individual photometric measurements to flux densities,
linearly interpolating between the points, and integrating. We also highlight
some specific areas where the UV flux can be mischaracterized.Comment: Accepted for publication in the Astronomical Journal. 16 pages, 9
figures. A PDF file with wide-screen friendly figures is linked from this
blog post
http://ultravioletsupernova.blogspot.com/2016/08/interpreting-flux-from-broadband.htm
SOUSA: the Swift Optical/Ultraviolet Supernova Archive
The Ultra-Violet Optical Telescope on the Swift spacecraft has observed
hundreds of supernovae, covering all major types and most subtypes. Here we
introduce the Swift Optical/Ultraviolet Supernova Archive (SOUSA), which will
contain all of the supernova images and photometry. We describe the observation
and reduction procedures and how they impact the final data. We show photometry
from well-observed examples of most supernova classes, whose absolute
magnitudes and colors may be used to infer supernova types in the absence of a
spectrum. A full understanding of the variety within classes and a robust
photometric separation of the groups requires a larger sample, which will be
provided by the final archive. The data from the existing Swift supernovae are
also useful for planning future observations with Swift as well as future UV
observatories.Comment: Accepted for publication in the UV issue of Astrophysics and Space
Science 10 pages, 6 figures SOUSA is an archive in progress with data being
posted to the Swift SN website:
http://swift.gsfc.nasa.gov/docs/swift/sne/swift_sn.htm
RE J2248-511 - Not all variable, ultrasoft, X-ray AGN have narrow Balmer lines
We present ASCA data on RE J2248-511, extending existing optical and soft
X-ray coverage to 10 keV, and monitoring the soft component. These data show
that, despite a very strong ultrasoft X-ray excess below 0.3 keV and a soft
0.3--2 keV spectral index in earlier ROSAT data, the hard X-ray spectrum
(alpha~ -0.8; 0.6-10 keV) is typical of type 1 AGN, and the soft component has
since disappeared. Optical data taken at two different epochs show that the big
blue bump is also highly variable. The strength of the ultrasoft X-ray
component and the extreme variability in RE J2248-511 are reminiscent of the
behaviour observed in many narrow line Seyfert 1s (NLS1s). However, the high
energy end of the ROSAT spectrum, the ASCA spectrum and the Balmer line full
widths at half maximum of ~3000 km/s in RE J2248-511, are typical of normal
Seyfert 1 AGN.
The change in the soft X-ray spectrum as observed in the ROSAT and ASCA data
is consistent with the behaviour of Galactic Black Hole Candidates (GBHCs) as
they move from a high to a low state, ie. a fall in the ultrasoft component and
a hardening of the X-ray continuum. This GBHC analogy has also been proposed
for NLS1s. Alternatively, the variability may be caused by opacity changes in a
hot, optically-thin corona which surrounds a cold, dense accretion disc; this
was first suggested by Guainazzi et al. for 1H0419-577, an object which shows
remarkably similar properties to RE J2248-511.Comment: 10 pages, 4 figures. Accepted for Monthly Notices of RA
Swift/UVOT Photometry of the Planetary Nebula WeBo 1: Unmasking A Faint Hot Companion Star
We present an analysis of over 150 ks of data on the planetary nebula WeBo 1
(PN G135.6+01.0) obtained with the Swift Ultraviolet Optical Telescope (UVOT).
The central object of this nebula has previously been described as a late-type
K giant barium star with a possible hot companion, most likely a young
pre-white dwarf. UVOT photometry shows that while the optical photometry is
consistent with a large cool object, the near-ultraviolet (UV) photometry shows
far more UV flux than could be produced by any late-type object. Using model
stellar atmospheres and a comparison to UVOT photometry for the pre-white dwarf
PG 1159-035, we find that the companion has a temperature of at least 40,000 K
and a radius of, at most, 0.056 R_sun. While the temperature and radius are
consistent with a hot compact stellar remnant, they are lower and larger,
respectively, than expected for a typical young pre-white dwarf. This likely
indicates a deficiency in the assumed UV extinction curve. We find that higher
temperatures more consistent with expectations for a pre-white dwarf can be
derived if the foreground dust has a strong "blue bump" at 2175 AA and a lower
R_V. Our results demonstrate the ability of Swift to both uncover and
characterize hot hidden companion stars and to constrain the UV extinction
properties of foreground dust based solely on UVOT photometry.Comment: 26 pages, 9 figure, accepted to Astronomical Journa
An Updated Ultraviolet Calibration for the Swift/UVOT
We present an updated calibration of the Swift/UVOT broadband ultraviolet
(uvw1, uvm2, and uvw2) filters. The new calibration accounts for the ~1% per
year decline in the UVOT sensitivity observed in all filters, and makes use of
additional calibration sources with a wider range of colours and with HST
spectrophotometry. In this paper we present the new effective area curves and
instrumental photometric zeropoints and compare with the previous calibration.Comment: 4 pages, 3 figures, 2 tables. Presented at GRB 2010 symposium,
Annapolis, November 2010 to be published in American Institute of Physics
Conference Serie
Large Binocular Telescope observations of PSR J2043+2740
We present the results of deep optical imaging of the radio/-ray
pulsar PSR J2043+2740, obtained with the Large Binocular Telescope (LBT). With
a characteristic age of 1.2 Myr, PSR J2043+2740 is one of the oldest (non
recycled) pulsars detected in -rays, although with still a quite high
rotational energy reservoir ( erg
s). The presumably close distance (a few hundred pc), suggested by the
hydrogen column density ( cm),
would make it a viable target for deep optical observations, never attempted
until now. We observed the pulsar with the Large Binocular Camera of the LBT.
The only object (V=25.440.05) detected within ~3" from the pulsar radio
coordinates is unrelated to it. PSR J2043+2740 is, thus, undetected down to
V~26.6 (3-), the deepest limit on its optical emission. We discuss the
implications of this result on the pulsar emission properties.Comment: 4 pages, 3 figures, accepted for publication on MNRA
Multi-wavelength observations of 3FGL J2039.6-5618: a candidate redback millisecond pulsar
We present multi-wavelength observations of the unassociated gamma-ray source
3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source
gamma-ray properties suggest that it is a pulsar, most likely a millisecond
pulsar, for which neither radio nor -ray pulsations have been detected
yet. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several
candidate X-ray counterparts within/close to the gamma-ray error box. The
brightest of these X-ray sources is variable with a period of 0.22450.0081
d. Its X-ray spectrum can be described by a power law with photon index
, and hydrogen column density cm, which gives an unabsorbed 0.3--10 keV X-ray flux of erg cm s. Observations with the Gamma-Ray Burst
Optical/Near-Infrared Detector (GROND) discovered an optical counterpart to
this X-ray source, with a time-average magnitude . The counterpart
features a flux modulation with a period of 0.227480.00043 d that
coincides, within the errors, with that of the X-ray source, confirming the
association based on the positional coincidence. We interpret the observed
X-ray/optical periodicity as the orbital period of a close binary system where
one of the two members is a neutron star. The light curve profile of the
companion star, with two asymmetric peaks, suggests that the optical emission
comes from two regions at different temperatures on its tidally-distorted
surface. Based upon its X-ray and optical properties, we consider this source
as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to
be a new redback system.Comment: 35 pages, 8 figures, accepted for publication on Astrophysical
Journa
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